When it comes to fighting climate change, electric buses pose a triple threat: they promote energy-efficient levels of urban population density; remove dozens of polluting vehicles from the streets; and does not release tailpipe emissions.
However, the popularity of this approach presents its own challenges: Cities can deploy electric buses faster than their power grids can meet growing demand.
For Xiaoyue Cathy Liu, an engineering professor at the University of Utah, this challenge is an opportunity not only to solve the immediate problem of network stability, but to radically rethink how public transportation systems are integrated in other parts of civic infrastructure.
“The integration of solar power generation and energy storage in bus stations introduces a new mode of renewable energy production and management,” Liu said, “transforming a public transportation station into an energy center that produces more electricity of what he consumes”.
Liu, a professor in the Department of Civil and Environmental Engineering at the Price College of Engineering, recently published a study in the journal Nature Energy analyzing the potential of this approach using data from Beijing’s electric bus fleet. The international collaboration includes researchers from China’s Beihang University, Sweden’s Chalmers University of Technology and Germany’s Fraunhofer Institute for Systems Research and Innovation ISI.
Beijing’s 27,000 buses form the largest public transportation system in the world. More than 90% of those in service in 2022 are low or zero emission vehicles. These battery-powered buses are recharged through a network of more than 700 bus stations spread across 6,500 square miles, a substantial piece of physical infrastructure that runs parallel to the region’s electrical grid. And given the power demands of the vehicles they serve, these tanks place a large burden on that grid, increasing the potential for localized blackouts or other disruptions.
Using advanced data science techniques, Liu and his colleagues are exploring whether locally generated solar power would be enough to offset this demand. Crucially, they are also studying the complicated economic factors that would determine the viability of this approach.
“More than meeting demand, our simulations show that these reservoirs could become energy producers, further stabilizing the grid,” Liu said.
The study is based on a computer model of Beijing’s bus network, packed with real-world data on air temperature and solar irradiance at each station, recorded throughout 2020. Combined with the rooftop surface of Each season, researchers able to predict the electrical output of solar panels that could be installed there.
Adding to the complexity of this model is the degree of variation between deposits, both in terms of supply and demand. With more buses to charge, busier stations can make the most of the day’s sunshine, while more remote stations would need to store or redistribute their excess electricity so it doesn’t go to waste.
“We found that energy storage is the most expensive factor in the model, so smarter and more strategic charging programs would need to be implemented,” Liu said. “That responsiveness is critical as variable energy pricing schemes have such a large impact on the overall economy.”
The researchers aim to further generalize their model, providing a path for other countries to estimate the return on investment of similarly transforming bus stations and other pieces of civic infrastructure into energy hubs.